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<H1 id="MPI_T_pvar_start">MPI_T_pvar_start</H1>
Start a performance variable 
<H2>Synopsis</H2>
<PRE>
</PRE>
<PRE>
int MPI_T_pvar_start(MPI_T_pvar_session session, MPI_T_pvar_handle handle)
</PRE>

<P>
<H2>Input Parameters</H2>
<DL>
<DT><B>session </B> <DD> identifier of performance experiment session (handle)

<DT><B>handle </B> <DD> handle of a performance variable (handle)
</DL>
<P>
<H2>Notes</H2>
If the constant MPI_T_PVAR_ALL_HANDLES is passed in handle, the MPI implementation
attempts to start all variables within the session identified by the parameter session for
which handles have been allocated. In this case, the routine returns MPI_SUCCESS if all
variables are started successfully, otherwise MPI_T_ERR_PVAR_NO_STARTSTOP is returned.
Continuous variables and variables that are already started are ignored when
MPI_T_PVAR_ALL_HANDLES is specified.
<P>
<H2>Thread and Interrupt Safety</H2>
<P>
This routine is thread-safe.  This means that this routine may be
safely used by multiple threads without the need for any user-provided
thread locks.  However, the routine is not interrupt safe.  Typically,
this is due to the use of memory allocation routines such as <tt>malloc
</tt>or other non-MPICH runtime routines that are themselves not interrupt-safe.
<P>
<H2>Errors</H2>
<P>
All MPI routines (except <tt>MPI_Wtime</tt> and <tt>MPI_Wtick</tt>) return an error value;
C routines as the value of the function and Fortran routines in the last
argument.  Before the value is returned, the current MPI error handler is
called.  By default, this error handler aborts the MPI job.  The error handler
may be changed with <tt>MPI_Comm_set_errhandler</tt> (for communicators),
<tt>MPI_File_set_errhandler</tt> (for files), and <tt>MPI_Win_set_errhandler</tt> (for
RMA windows).  The MPI-1 routine <tt>MPI_Errhandler_set</tt> may be used but
its use is deprecated.  The predefined error handler
<tt>MPI_ERRORS_RETURN</tt> may be used to cause error values to be returned.
Note that MPI does <em>not</em> guarantee that an MPI program can continue past
an error; however, MPI implementations will attempt to continue whenever
possible.
<P>
<DL>
<DT><B>MPI_SUCCESS </B> <DD> No error; MPI routine completed successfully.
</DL>
<DL>
<DT><B>MPI_T_ERR_INVALID_HANDLE </B> <DD> The handle is invalid.
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<DT><B>MPI_T_ERR_INVALID_SESSION </B> <DD> Session argument is not valid.
</DL>
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<DT><B>MPI_T_ERR_NOT_INITIALIZED </B> <DD> The MPI tool information interface is not initialized.
</DL>
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<DT><B>MPI_T_ERR_PVAR_NO_STARTSTOP </B> <DD> The performance variable can not be started or stopped.
</DL>
<DL>
<DT><B>MPI_ERR_OTHER </B> <DD> Other error; use <tt>MPI_Error_string</tt> to get more information
about this error code. 
</DL>
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